Feature request: Only enable on staging / test site

Hey! Thank you for a fine little plugin! I appreciate its simplicity.

I’m using it on staging / test sites, and of course, I’m whitelisting my IP.

My fear is, that I some day, push my staging site to the live URL, and forget to disable the “Under Construction” option (or plugin), and not notice, as my IP is whitelisted.

So, I’d fancy an option that either:

1. Only enable Under Construction on dev. / test. / staging. subdomains, example “staging.example.net”.
2. Never enable Under Construction when on running on the live url; example “www.example.net”. Would probably require another input field for the live URL.

Does that make sense? I’d be happy to beta test.